FIG. 9 shows a conventional water pipe structure for RV. A pipe assembly installed inside a camping car comprises a plurality of hard pipes 21 in cooperation with T-shaped branching connectors 22, a plurality of retaining rings 23, a plurality of control valve heads 24, and a plurality of corner connectors 25. The hard pipes 21 are cut for a required length according to the corner of the installation space and then fixedly connected with the T-shaped branching connectors 22 and the retaining rings 23. The ends of the hard pipes 22 are connected with the control valve heads 24 through the retaining rings 23, respectively. The piping arrangement of the hard pipes 21 must be fitted with the RV body structure in the form of an edge wiring. At the corners, it is necessary to use the T-shaped branching connectors 22 in cooperation with the retaining rings 23. This way is inconvenient for piping, and the required parts and the labor cost are increased. The pipe structure is unable to provide a simply way for the user to identify the purpose of each pipe. It is easy to make a mistake in the connection of the pipes. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve this problem.